How to grow Cosmos in the UK
Feathery leaves and pink, white and purple daisies from July to the first frost.
- DifficultyEasy peasy
- WhereBeds or Pots
- Sunfull sun
- Grows to100cm
- Spacing40cm
- Time to first pickabout 12 weeks
- Typeannual
When to sow, plant and harvest cosmos
| Sow indoors | mid March to late April |
|---|---|
| Plant out | mid May to late June |
| In flower | early July to mid October |
Dates are for central England. Sow about two weeks later in the north and Scotland, and up to two weeks earlier in the south and south west. Get the dates for your postcode.
Starting it indoors
- Fill a small pot or tray with seed compost
- Push the seeds in (1cm deep) - a couple per pot
- Water gently, then put them on a bright windowsill
- Keep the compost damp but not soggy - check it every day
- When they have 2 proper leaves, give each seedling its own pot
Planting it out
- Toughen them up ('hardening off'): put them outside in the day for a week, bring them in at night
- Dig a hole a bit bigger than the pot
- Tip the plant out gently, holding the leaves, not the stem
- Pop it in the hole, firm the soil around it, and water well
- Space the plants about 40cm apart each way
Top tips for growing cosmos
- Don't feed them - rich soil gives leaves, not flowers.
Looking after cosmos
- Week 4: Snip off dead cosmos flowers so new ones keep coming
Soil and feeding
Poor soil - really!. Nasturtiums flower best in poor soil. Feed them and you get all leaves and no flowers.
Pests and problems
- Slugs & snails: munch seedlings overnight, worst in wet weather
- Protect young plants from slugs for the first couple of weeks
Harvesting and eating cosmos
Cut them for a vase when the buds are just opening.
Companion planting
Grows well with
- Cherry tomatoes: brings hoverflies and lacewings, which eat greenfly
- Big tomatoes: brings hoverflies and lacewings, which eat greenfly
- French beans: brings hoverflies that eat blackfly
- Kale: brings hoverflies and tiny wasps that eat pests
- Strawberries: brings bees for more berries
Saving your own cosmos seed
Late summer and autumn, as the flowers fade.
- Stop deadheading a few flowers - let them fade on the plant
- When the seed heads are dry and brown (and the seeds rattle), snip them off on a dry day
- Shake the seeds into a paper bag
- Spread on a plate to dry for a week
Where to buy cosmos seeds
Thompson & Morgan · Suttons · Amazon
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Cosmos questions
When should I sow cosmos in the UK?
In the UK, sow cosmos indoors from mid March to late April. These dates suit central England; sow about two weeks later in the north and Scotland and up to two weeks earlier in the mild south and south west.
When do I plant out cosmos?
Plant cosmos out from mid May to late June, once the last frost has passed.
When can I enjoy cosmos?
Cosmos is ready from early July to mid October. Cut them for a vase when the buds are just opening.
How long do cosmos take to grow?
Roughly 12 weeks from sowing or planting until the first harvest.
Are cosmos easy to grow?
Cosmos are rated 'easy peasy' for beginners, and can be grown in the ground or a raised bed or in pots and containers.
Plan your own garden: it tells you what to do and when, for your postcode.
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